Nexus has no single permanent address and no clearnet site. It publishes several onion addresses, all resolving to the same market. Copy a current one from this page, open it in Tor Browser, and verify it against the login captcha.
The market rotates its onion addresses so a flood or takedown on one never puts it out of reach. Bookmark this page rather than a single raw address, and copy the current one when you need it.
Monero by default for privacy, Litecoin for small orders where Bitcoin fees are steep, and Bitcoin only when a vendor requires it. The deposit address is fresh per order.
Copy the address from this page, then hold it against the address the login captcha prints. Match means genuine, mismatch means close the tab. Never type a fifty-six character onion from memory.
No. A genuine login never asks for the recovery phrase. A page that does is a phishing clone. Close the tab and reach the market through a verified address.
Build a fresh Tor circuit and retry, or switch to another address here. All resolve to the same market. If every address stalls for several minutes, wait a short while, because floods pass.